Magnetic memory and manufacturing method thereof

ABSTRACT

According to one embodiment, a magnetic memory is disclosed. The magnetic memory includes a substrate, and a contact plug provided on the substrate. The contact plug includes a first contact plug, and a second contact plug provided on the first contact plug and having a smaller diameter than that of the first contact plug. The magnetic memory further includes a magnetoresistive element provided on the second contact plug. The diameter of the second contact plug is smaller than that of the magnetoresistive element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/804,517, filed Mar. 22, 2013, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic memoryhaving a magnetoresistive element and a manufacturing method thereof.

BACKGROUND

In recent years, a semiconductor memory with a resistance change elementsuch as a PRAM (phase-change random access memory) or an MRAM (magneticrandom access memory), has been attracting attention and beingdeveloped, in which the resistance change element is utilized as amemory element. The MRAM is a device which performs a memory operationby storing “1” or “0” information in a memory cell by using amagnetoresistive effect, and has such features as nonvolatility,high-speed operation, high integration and high reliability.

A large number of MRAMs, which use elements exhibiting a tunnelingmagnetoresistive (TMR) effect, among other magnetoresistive effects,have been reported. One of magnetoresistive effect elements is amagnetic tunnel junction (MTJ) element including a three-layermultilayer structure of a recording layer having a variablemagnetization direction, an insulation film as a tunnel barrier, and areference layer which maintains a predetermined magnetization direction.

The resistance of the MTJ element varies depending on the magnetizationdirections of the recording layer and reference layer. When thesemagnetization directions are parallel, the resistance takes a minimumvalue, and when the magnetization directions are antiparallel, theresistance takes a maximum value, and information is stored byassociating the parallel state and antiparallel state with binaryinformation “0” and binary information “1”, respectively.

Write of information to the MTJ element involves a magnetic-field writescheme in which only the magnetization direction in the recording layeris inverted by a current magnetic field resulting from a current flowingthrough a write wire and a write (spin injection write) scheme usingspin angular momentum movement in which the magnetization direction inthe recording layer is inverted by passing a spin polarization currentthrough the MTJ element itself.

In the former scheme, when the element size is reduced, the coercivityof a magnetic body constituting the recording layer increases and thewrite current tends to increase, and thus it is difficult to achieveboth the miniaturization and reduction in electric current.

On the other hand, in the latter scheme (spin injection write scheme),as the volume of the magnetic layer constituting the recording layerbecomes smaller, the number of spin-polarized electrons to be injected,may be smaller, and thus it is expected that both the miniaturizationand reduction in electric current can be easily achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a magneticmemory according to a first embodiment;

FIG. 2 is a cross-sectional view for explaining a manufacturing methodof the magnetic memory according to the first embodiment;

FIG. 3 is a cross-sectional view for explaining the manufacturing methodof the magnetic memory according to the first embodiment following FIG.2;

FIG. 4 is a cross-sectional view for explaining the manufacturing methodof the magnetic memory according to the first embodiment following FIG.3;

FIG. 5 is a cross-sectional view for explaining the manufacturing methodof the magnetic memory according to the first embodiment following FIG.4;

FIG. 6 is a cross-sectional view for explaining the manufacturing methodof the magnetic memory according to the first embodiment following FIG.5;

FIG. 7 is a cross-sectional view for explaining a problem of amanufacturing method of a magnetic memory of a comparative example;

FIG. 8 is a cross-sectional view schematically illustrating a magneticmemory according to a second embodiment;

FIG. 9 is a cross-sectional view for explaining a manufacturing methodof the magnetic memory according to the second embodiment;

FIG. 10 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the second embodimentfollowing FIG. 9;

FIG. 11 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the second embodimentfollowing FIG. 10;

FIG. 12 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the second embodimentfollowing FIG. 11;

FIG. 13 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the second embodimentfollowing FIG. 12;

FIG. 14 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the second embodimentfollowing FIG. 13;

FIG. 15 is a cross-sectional view schematically illustrating a magneticmemory according to a third embodiment;

FIG. 16 is a plan view schematically illustrating a magnetic memoryaccording to the third embodiment;

FIG. 17 is a cross-sectional view for explaining a manufacturing methodof the magnetic memory according to the third embodiment;

FIG. 18 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the third embodimentfollowing FIG. 17;

FIG. 19 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the third embodimentfollowing FIG. 18;

FIG. 20 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the third embodimentfollowing FIG. 19;

FIG. 21 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the third embodimentfollowing FIG. 20;

FIG. 22 is a cross-sectional view schematically illustrating a magneticmemory according to a fourth embodiment;

FIG. 23 is a plan view schematically illustrating a magnetic memoryaccording to the fourth embodiment;

FIG. 24 is a cross-sectional view for explaining a manufacturing methodof the magnetic memory according to the fourth embodiment;

FIG. 25 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the fourth embodimentfollowing FIG. 24;

FIG. 26 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the fourth embodimentfollowing FIG. 25;

FIG. 27A is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the fourth embodimentfollowing FIG. 26;

FIG. 27B is a plan view for explaining the manufacturing method of themagnetic memory according to the fourth embodiment following FIG. 26;

FIG. 28A is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the fourth embodimentfollowing FIG. 27A;

FIG. 28B is a plan view for explaining the manufacturing method of themagnetic memory according to the fourth embodiment following FIG. 27B;

FIG. 29A is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the fourth embodimentfollowing FIG. 28A;

FIG. 29B is a plan view for explaining the manufacturing method of themagnetic memory according to the fourth embodiment following FIG. 28B;

FIG. 30 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the fourth embodimentfollowing FIG. 29A;

FIG. 31 is a cross-sectional view for explaining the manufacturingmethod of the magnetic memory according to the fourth embodimentfollowing FIG. 30; and

FIG. 32 is a cross-sectional view for explaining a variation of themagnetic memory according to the fourth embodiment.

DETAILED DESCRIPTION

Embodiments will now be described with reference to the drawings. In thedescription recited below, members corresponding to the members alreadydescribed are marked with like reference numerals and a detaildescription is omitted as appropriate.

In general, according to one embodiment, a magnetic memory is disclosed.The magnetic memory includes a substrate and a contact plug provided onthe substrate. The contact plug includes a first contact plug and asecond contact plug provided on the first contact plug and having asmaller diameter than that of the first contact plug. The magneticmemory further includes a magnetoresistive element provided on thesecond contact plug. The diameter of the second contact plug is smallerthan that of the magnetoresistive element.

According to another embodiment, a method for manufacturing a magneticmemory is disclosed. The method includes forming a first insulating filmon a substrate, forming a first contact plug in the first insulatingfilm, and forming a second insulating film on the first insulating film.The method further includes forming a second contact plug connecting tothe first contact plug in the second insulating film. The second contacthas a smaller diameter than the of the first contact plug. The methodfurther includes forming stacked films, which are to be processed into amagnetoresistive element on the second contact plug and the secondinsulating film, and forming the magnetoresistive element by processingthe stacked film.

First Embodiment

FIG. 1 is a cross-sectional view schematically illustrating a magneticmemory according to a first embodiment.

In FIG. 1, 100 denotes a silicon substrate (a semiconductor substrate),and an isolation region 101 is formed on a surface of the siliconsubstrate 100. A selection transistor 10 is formed on a region (activearea) separated by the isolation region 101. As the selection transistor10, a planar MOS transistor is shown in FIG. 1, but an SGT (SurroundingGate Transistor) may be used.

The selection transistor 10 includes a gate insulating film 102 formedon the surface of the silicon substrate 100, a gate electrode 103 formedon the gate insulating film 102, and a pair of source and drain regions104 formed so as to sandwich the gate electrode 103.

The selection transistor 10 is an element for selecting an MTJ element20. One of the source and drain regions 104 of the selection transistor10 is connected to an MTJ element 20 via a contact plug 150 (151, 152).The planar shape of the contact plug 150 (151, 152) and the MTJ element20 are, for example, a circular shape.

The contact plug 150 includes a lower contact plug (a first contactplug) 151 and an upper contact plug (a second contact plug) 152 that isprovided on a central area of the upper surface of the lower contactplug 151 and has a diameter smaller than that of the lower contact plug151. The contact plug 150 is provided in an interlayer insulating film180 (interlayer insulating films 181, 182, and 183). The upper surfaceof the interlayer insulating film 180 is planar.

The other of the source and drain regions 104 of the selectiontransistor 10 is connected to a wiring 170 via a contact plug 160. Thecontact plug 160 is provided in the interlayer insulating film 181 andthe wiring 170 is provided in the interlayer insulating film 182.

The MTJ element 20 includes a lower electrode 201, a storage layer 202,a tunnel barrier layer 203, a reference layer 204, a shift adjustmentlayer 205, a capping layer 206, and an upper electrode 207. Thethickness of the storage layer 202 is, for example, 1 nm. The thicknessof the tunnel barrier layer 203 is, for example, 1 nm. The diameter ofthe MTJ element is, for example, 34 nm. The shift adjustment layer 205has a function to lessen and adjust a shift of switching current in thestorage layer 202 caused by a leakage magnetic field from the referencelayer 204.

The MTJ element 20 having the top pin structure is shown in FIG. 1shows, but the present embodiment is effective in a case of an MTJelement having a bottom pin structure. That is, the present embodimentis effective regardless of the structure of the MTJ element.

The lower electrode 201 of the MTJ element 20 is connected to an uppersurface of the upper contact plug 152. The upper surface of the uppercontact plug 152 is covered by the lower electrode 201. The diameter ofthe upper contact plug 152 is smaller than the diameters of the lowercontact plug 151 and the MTJ element 20. In the case of a 1 Gb MRAMcell, for example, the diameter of the upper contact plug 152 is 5 nm,the diameter of the lower contact plug 151 is 50 nm, and the diameter ofthe MTJ element 20 is 35 nm.

Since the diameter of the upper contact plug 152 is relatively small asjust described, the planarity of the upper surface of the upper contactplug 152 is secured. As a result, the upper surface of the upper contactplug 152 and the upper surface of the interlayer insulating film 180exist in the substantially same plane. That is, an underlying layer ofthe lower electrode 201 (the upper surfaces of the upper contact plug152 and the interlayer insulating film) is flat.

In general, a characteristic of the MTJ element is sensitive to theflatness of the underlying layer. In the present embodiment, since theunderlying layer of the lower electrode 201 has a flat surface asdescribed above, the degradation of the characteristic of the MTJelement 20 is suppressed.

Moreover, the diameter of the lower contact plug 151 also need not belarger than the diameter of the MTJ element 20, the lower contact plug151 does not prevent the magnetic memory from being downscaled.

The magnetic memory of the present embodiment will be further describedbelow by following a manufacturing process of the magnetic memory of thepresent embodiment.

First, as shown in FIG. 2, the isolation region 101, the selectiontransistor 10, the interlayer insulating film 181, the contact plug 160,the interlayer insulating film 182, and the wiring 170 are formed on thesilicon substrate 100 using well-known methods.

Next, as shown in FIG. 3, an interlayer insulating film 183 a is formedover the entire surface, a contact hole is formed in the interlayerinsulating films (the first insulating film) 183 a, 182, and 181,hereafter a conductive film 151 to be processed into the lower contactplug is formed over the entire surface. The conductive film 151 isformed so as to fill the contact hole.

A material (a first material) of the conductive film 151 (the lowercontact plug) includes, for example, tungsten (W), copper (Cu), andtitanium nitride (TiN). In the case of using W or Cu, the contact holeis filled with the conductive film 151 after a barrier metal film isformed on inner surfaces (bottom surface and side surface) of thecontact hole. This barrier metal film may be, for example, a singlelayer film of a titanium (Ti) film or a titanium nitride (TiN) film, ora stacked film of a Ti film and a TiN film.

Next, as shown in FIG. 4, by using CMP (Chemical Mechanical Polishing)process, the lower contact plug 151 outside the contact hole is removedto form the lower contact plug 151, and the surfaces of the interlayerinsulating film 183 a and the lower contact plug 151 are planarized.

Next, as shown in FIG. 5, an interlayer insulating film 183 b (a secondinsulating film) is formed on the entire surface (the region includingthe lower contact plug 151 and the interlayer insulating film 183 a), acontact hole is formed in the interlayer insulating film 183 b, and aconductive film 152 to be processed into the upper contact plug isformed on the entire surface so as to fill the contact hole. Thereafter,as in the case of the lower contact plug 151, an upper contact plug 152is formed and the surfaces of the interlayer insulating film 183 b andthe upper contact plug 152 are planarized by using CMP process.

A material (a second material) of the conductive film (the upper contactplug) 152 includes, for example, at least one of tantalum (Ta), silicon(Si), Ti, Cu, W, Al, hafnium (Hf), boron (B), cobalt (Co), and carbonnanotube. Si is, for example, polycrystalline silicon (poly-Si).

In the case of using W or Cu as the material of the conductive film 152,the contact hole is filled with the conductive film 152 after a barriermetal film is formed first on the inner surfaces (the bottom surface andside surface) of the contact hole. This barrier metal film may be, forexample, a single layer film of a Ti film or a TiN film, or a stackedfilm of a Ti film and a TiN film.

An increasing of contact resistance between the MTJ element 20 (thelower electrode 201) and the upper contact plug 152 is suppressed byselecting a material having a resistance lower than that of lowercontact plug 151 as a material of the upper contact plug 152. Thematerial of the lower contact plug 151 and the material of the uppercontact plug 152 may be the same if a sufficient contact resistance issecured.

In the manufacturing method of the present embodiment, the stacked filmof the interlayer insulating film 183 a and the interlayer insulatingfilm 183 b corresponds to the interlayer insulating film 183 in FIG. 1.

Next, as shown in FIG. 6, the magnetic memory structure shown in FIG. 1is obtained by using well-known processes, which includes formingstacked films 20 (indicated as a single layer film in FIG. 6) to beprocessed into the MTJ element on the interlayer insulating film 183 andthe upper contact plug 152, forming an etching mask 30 on the stackedfilm 20, and processing the stacked film 20 by IBE (Ion Beam Etching)using the etching mask 30 as a mask to form the MTJ element 20. A dryetching method other than IBE, for example, RIE (Reactive Ion Etching)may be used.

The etching mask 30 is, for example, a hard mask. Processes for formingthe hard mask include, for example, a process for forming an insulatingfilm to be processed into the hard mask, a process for forming a resistpattern on the insulating film, and a process for transferring thepattern of the resist pattern to the insulating film by etching theinsulating film using the resist pattern as a mask.

In the present embodiment, no contact plug exists on a underlying layerof the stacked film 20 except a part covered by the etching mask 30,then a conductive material which arises from the etching of the contactplug does not adhere on a sidewall of the MTJ element. Thereby, aproblem of a short-circuit between the storage layer and the referencelayer due to the adhesion of the conductive material onto the sidesurface of the storage layer, the side surface of the tunnel barrierlayer and side surface of the reference layer of the MTJ element doesnot arise.

In contrast, in the case of a comparative example, as shown in FIG. 7, adiameter of the contact plug 150 is larger than the diameter of the MTJelement. Therefore, the material of the contact plug 150 adheres ontothe side surface of the MTJ element during the processing of the stackedfilm which are be processed into the MTJ element, and a layer 41 whichcauses the short-circuit between the storage layer 202 and the referencelayer 204 is formed on the side surface of the MTJ element.

The reason for the diameter of the contact plug 150 being larger thanthe diameter of the MTJ element in the comparative example is asfollows.

As described above, the characteristic of the MTJ element is sensitiveto the flatness of the underlying layer. The underlying layer formed ofthe upper surface of the contact plug 150 and the upper surface of theinterlayer insulating film 180 have a level difference 43. The reasonthe level difference 43 arises that there exists difference between aCMP rate of the contact plug 150 (metal) and a CMP rate of theinterlayer insulating film 180 (dielectric material). As shown in FIG.7, the CMP for securing the flatness of the underlying of the MTJelement may cause the level difference 43 at the outside of the MTJelement. Therefore, the diameter of the contact plug 150 is set to belarger than the diameter of the MTJ element in the comparative example.In the comparative example, scaling down of the magnetic memory isprevented by the contact plug 150 since the diameter of the contact plug150 is larger than the diameter of the MTJ element.

Second Embodiment

FIG. 8 is a cross-sectional view schematically illustrating a magneticmemory according to a second embodiment.

The present embodiment is different from the first embodiment in thatthe side surface of the upper contact plug 152 is covered with aninsulating film 184 (a second insulating film). A material of theinsulating film 184 is different from the material of the interlayerinsulating film 183 (the first insulating film) covering the sidesurface of the lower contact plug 151.

For example, when the material of the interlayer insulating film 183 issilicon oxide, the material of the insulating film 184 is siliconnitride. In this case, the insulating film 184 functions as a CMPstopper in the CMP process of the conductive film to be processed intothe upper contact plug 152, as described later.

Moreover, when the material of the interlayer insulating film 183 issilicon oxide and the material of the upper contact plug 152 is Al, thematerial of the insulating film 184 is Al₂O₃. In this case, the materialof the insulating film 184 and the material of the upper contact plug152 include the same element (Al). When the material of the interlayerinsulating film 183 is silicon nitride, this silicon nitride and thematerial of the upper contact plug 152 have a common element. By usingthe common element, the CMP rate of the insulating film 184 can beapproximated to the CMP rate of the upper contact plug 152. As a result,in the above CMP process, the flatness of the underlying layer of theMTJ element 20 is improved, in which the underlying layer is formed ofthe upper surface of the upper contact plug 152 and the upper surface ofpart of the insulating film 184 around the upper contact plug 152.

The material of the lower contact plug 151 and the material of the uppercontact plug 152 may be the same, or different.

FIGS. 9 to 14 are cross-sectional views illustrating a manufacturingmethod of the magnetic memory according to the present embodiment. Themanufacturing method of the present embodiment is same as themanufacturing methods of the first embodiment up to the process offorming the interlayer insulating film 183. Thus, in the presentembodiment, manufacturing processes after the interlayer insulating film183 is formed will be described. For the sake of simplicity, the partslower than the upper part of interlayer insulating film 183 are omittedin FIGS. 9 to 14.

As shown in FIG. 9, the first contact hole is formed in the interlayerinsulating film 183, thereafter the lower contact plug 151 is buried inthe first contact hole by a well-known method (deposition of aconductive film and CMP). The material of the lower contact plug 151 is,for example, titanium nitride (TiN).

Next, as shown in FIG. 10, the upper part of the lower contact plug 151is removed by etching back the lower contact plug 151. As a result,upper part of the first contact hole is changed into a trench 71 whichis not filled with the first contact plug. The upper part of the lowercontact plug 151 is removed by an amount corresponding to the height ofthe upper contact plug.

Next, as shown in FIG. 11, an insulating film 184 is formed on thesurfaces of the lower contact plug 151 and the interlayer insulatingfilm 183. The trench is filled with the insulating film 184.

A concave portion 72 is formed in the surface of the insulating film 184due to the influence of the trench. The insulating film 184 is formedsuch that the diameter of the concave portion 72 is to be the same asthe diameter of the upper contact plug (for example, 10 nm or less). Thethickness of the insulating film 184 is, for example, 20 nm. Theinsulating film 184 can be formed, for example, by using ALD (AtomicLayer Deposition) process.

Next, as shown in FIG. 12, the insulating film 184 outside the trench 71and the insulating film 184 under the concave portion are removed byetching back the insulating film 184. As a result, a second contact holethat reaches the lower contact plug 151 is formed in the insulating film184 in a self-alignment manner.

Next, as shown in FIG. 13, a conductive film 152 to be processed into anupper contact plug is formed over the entire surface, so that the secondcontact hole is filled with the conductive film 152.

Next, as shown in FIG. 14, the conductive film 152 outside the secondcontact hole is removed by CMP process. During this CMP process, theinsulating film 184 is used as a CMP stopper. Consequently, the uppercontact plug 152 and the insulating film 184 having flat surfaces areformed. Thereafter, the well-known MTJ process (such as forming stackedfilms to be processed into the magnetoresistive element on the uppercontact plug 152 and the insulating film 184, forming themagnetoresistive element by processing the stacked film by using dryetching).

Third Embodiment

FIG. 15 is a cross-sectional view schematically illustrating a magneticmemory according to a third embodiment. For the sake of simplicity, theparts lower than the upper part of the interlayer insulating film 183are omitted in FIG. 15. FIG. 15 corresponds to the cross-sectional viewalong arrows 15-15 in FIG. 16.

The present embodiment is different from the second embodiment in thatan upper contact plug 152 a in the present embodiment has a hollowstructure where a hollow space exists along the height direction. Here,the hollow structure is a hollow cylinder. The upper contact plug 152 inthe first embodiment is a solid such as a cylinder or cuboid that has nohollow space.

The difference between the outer radius (R1) and the internal radius(R2) of the upper contact plug 152 a of the present embodiment (R1-R2)corresponds to the diameter of the upper contact plug 152 of the firstembodiment. In this case, the contact area between the upper contactplug 152 a and the lower electrode 201 of the MTJ element 20 of thepresent embodiment is larger than the contact area between the uppercontact plug 152 and the lower electrode 201 of the MTJ element 20 ofthe first embodiment. The upper contact plug 152 a of the presentembodiment has an advantage in reducing contact resistance.

In case of the present embodiment, as shown in FIG. 15, the uppercontact plug 152 a have two connection portions with the lower contactplug 151 in a cross section of the upper contact plug 152 a and thelower contact plug 151 taken along the plane defined by a normal lineperpendicular to a stacking direction of the upper contact plug 152 aand the lower contact plug 151.

FIGS. 17 to 21 are cross-sectional views illustrating a manufacturingmethod of the magnetic memory according to the present embodiment.

First, as the second embodiment, processes of FIGS. 9 and 10 areperformed.

Next, as shown in FIG. 17, an insulating film 184 (a second insulatingfilm) is formed on surfaces of the lower contact plug 151 and theinterlayer insulating film 183 (the first insulating film). Theinterlayer insulating film 183 and the material of the insulating film184 are respectively formed of different materials. As an example ofmaterial of the insulating film 184, a material which functions as a CMPstopper for CMP process (FIG. 21) may be used.

The trench 71 is filled with the insulating film 184. A concave portion72 a is formed on the surface of the insulating film 184 due to thetrench 71 (underlying layer). The insulating film 184 is formed so thatthe diameter of the concave portion 72 a is twice as large as the outerradius R1. The insulating film 184 can be formed by using, for example,ALD process.

Next, as shown in FIG. 18, the insulating film 184 outside the trench 71and the insulating film 184 under the concave portion are removed byetching back the insulating film 184. As a result, an opening portionthat reaches the first contact plug 171 and has a diameter twice aslarge as the outer radius of the upper contact plug is formed in theinsulating film 184 in a self-alignment manner.

Next, as shown in FIG. 19, a conductive film 152 a to be processed intoan upper contact plug is formed over the entire surface without fill theconcave portion, thereafter the conductive film 152 a is etched back.This etch-back process removes the conductive film 152 a in a centralportion of trench 71. The diameter of the central portion of trench 71corresponds to a diameter twice as large as the internal radius R1.

Next, as shown in FIG. 20, an insulating film 184 (a third insulatingfilm) is formed over the entire surface again. The central portion oftrench is filled with the insulating film 184. In the process, thethickness of the insulating film 184 is chosen so that the upper surfaceof the insulating film 184 is to be substantially planar.

Next, as shown in FIG. 21, an upper contact plug 152 a having a hollowcylinder structure is formed by polishing the insulating film 184 andthe conductive film 152 a by using CMP process. Thereafter, well-knownMTJ process (such as forming a stacked films to be a magnetoresistiveelement on the upper contact plug 152 a and the insulating film 184,forming the magnetoresistive element by processing the stacked films byusing dry etching) follows.

The insulating film 184 around the upper contact plug 152 a may be theinterlayer insulating film 183 as the first embodiment.

Fourth Embodiment

FIG. 22 is a cross-sectional view schematically illustrating a magneticmemory according to a fourth embodiment. FIG. 22 corresponds to thecross-sectional view along arrows 23-23 in FIG. 23.

The present embodiment is different from the first embodiment in that anupper contact plug 152 b of the present embodiment includes athree-dimensional structure in a form of the letter L (an L-shapedstructure). This L-shaped structure exists under the MTJ element 20.Each of two adjacent MTJ elements is provided with the upper contactplug 152 b. In the following description, the MTJ element 20 shown onthe left side in FIG. 22 is referred to as a first MTJ element, and theMTJ element on the right side is referred to as a second MTJ element.

Since there are an infinite number of planes defined by normal linesperpendicular to the height direction of upper contact plug 152 a, therealso exist an infinite number of cross sections of the upper contactplug 152 a defined by normal lines perpendicular to the height directionof upper contact plug 152 a. However, as shown in FIG. 22, there existsa cross section in which the shape of the upper contact plug 152 a isthe letter L-shaped. For example, as shown in FIG. 22, the shape of theletter L exists in the cross section taken along a line connecting twoadjacent MTJ elements.

FIGS. 24 to 31 are cross-sectional views illustrating a manufacturingmethod of the magnetic memory according to the present embodiment. Themanufacturing method of the present embodiment is same as themanufacturing methods of the first embodiment up to the process offorming the interlayer insulating film 183. Thus, in the presentembodiment, manufacturing processes after the interlayer insulating film183 is formed will be described. For the sake of simplicity, the partslower than the upper part of interlayer insulating film 183 are omittedin FIGS. 24 to 31.

As shown in FIG. 24, a lower contact plug 151 for the first MTJ element(hereinafter, referred to as lower contact plug for 1MTJ) and a contactplug 151 for the second MTJ element (hereinafter, referred to as lowercontact plug for 2MTJ) are formed in the interlayer insulating film 183by well-known methods (opening a contact hole, forming a conductivefilm, CMP for the conductive film).

Next, as shown in FIG. 25, the upper part of the interlayer insulatingfilm 183 c between the lower contact plug for 1MTJ 151 and the lowercontact plug for 2MTJ 151, an upper portion of the lower contact plugfor 1MTJ 151 on the side of the interlayer insulating film 183 c, and anupper portion of the lower contact plug for 2MTJ 151 are removed by anamount corresponding to the height of the upper contact plug.

As a result, a trench 81 is formed on the surfaces of the lower contactplug for 1MTJ 151, the lower contact plug for 2MTJ 151, and theinterlayer insulating film 183. An area of trench 81 is large since thetrench 81 is provided on areas corresponding to two MTJ elements and theinterlayer insulating film 183 c therebetween.

Next, as shown in FIG. 26, a conductive film 152 to be processed intoupper contact plugs is formed over the entire surface. Though the bottomsurface and side surface of the trench 81 are covered with theconductive film 152, the trench 81 is not filled with the conductivefilm 152. The conductive film 152 can be formed on the side surface ofthe trench 81 with precision since the trench 81 is large as describedabove. That is, it is possible to form a uniformly thin conductive film152 on the side surface of the trench 81. This is advantage forminiaturizing the magnetic memory.

Next, as shown in FIGS. 27A and 27B, an insulating film 185 is formed onthe conductive film 152, thereafter a resist pattern 31, which is usedfor processing a conductive film 152 to be an upper contact plug, isformed on the insulating film 185.

Next, as shown in FIGS. 28A and 28B, the surface of the interlayerinsulating film 183 is exposed by etching the insulating film 185 andthe conductive film 152 using the resist pattern 31 as a mask. After theetching, the resist pattern 31 is removed.

Next, as shown in FIGS. 29A and 29B, the upper contact plug 152 for thefirst MTJ element and the upper contact plug 152 for the second MTJelement are formed by etching back process the insulating film 185, theconductive film 152, and the interlayer insulating film 183.

Next, as shown in FIG. 30, an insulating film 186 is formed over theentire surface so as to fill the concave portion formed on the surfaceshown in FIG. 29A. Materials of the insulating films 186 and 185 may besame, or may be different. For example, a material easily polished byCMP process (silicon oxide) is used as the material of insulating film186, and a material usable as a CMP stopper (silicon nitride) is used asthe material of insulating film 185.

Next, as shown in FIG. 31, the insulating film 186 is polished by CMPprocess, and the upper surface of the upper contact plug 152 is exposed.Thereafter, the well-known MTJ process follows.

The present embodiment (FIG. 23) explains a case where two contact plugsconnecting to the lower electrodes adjacent MTJ elements aresimultaneously formed, however as shown in FIG. 32, four contact plugsconnecting to lower electrodes of four MTJ elements arranged at fourpositions corresponding to four apexes of a rectangle.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic memory comprising: a substrate; acontact plug provided on the substrate, the contact plug including afirst contact plug, and a second contact plug provided on the firstcontact plug and having a smaller diameter than a diameter of the firstcontact plug, and the first and second contact plugs comprising a samematerial; and a magnetoresistive element provided on the second contactplug, wherein the diameter of the second contact plug is smaller than adiameter of the magnetoresistive element.
 2. The magnetic memoryaccording to claim 1, wherein an upper surface of the second contactplug is covered with the magnetoresistive element.
 3. A magnetic memorycomprising: a substrate; a contact plug provided on the substrate, thecontact plug including a first contact plug, and a second contact plugprovided on the first contact plug and having a smaller diameter than adiameter of the first contact plug, the first contact plug comprising afirst material, and the second contact plug comprising a second materialdiffering from the first material; and a magnetoresistive elementprovided on the second contact plug, wherein the diameter of the secondcontact plug is smaller than a diameter of the magnetoresistive element.4. The magnetic memory according to claim 3, wherein the second materialis lower in resistance than the first material.
 5. The magnetic memoryaccording to claim 3, wherein the second material includes at least oneof tantalum, silicon, titanium, copper, tungsten, aluminum, hafnium,boron, nickel, cobalt, and carbon nanotube.
 6. A magnetic memorycomprising: a substrate; a contact plug provided on the substrate, thecontact plug including a first contact plug, and a second contact plugprovided on the first contact plug and having a smaller diameter than adiameter of the first contact plug; and a magnetoresistive elementprovided on the second contact plug, wherein the diameter of the secondcontact plug is smaller than a diameter of the magnetoresistive element,wherein a side surface of the first contact plug is covered with a firstinsulating film, and a side surface of the second contact plug iscovered with a second insulating film of a material differing from amaterial of the first insulating film.
 7. The magnetic memory accordingto claim 6, wherein the second insulating film includes an elementconstituting the second contact plug.
 8. The magnetic memory accordingto claim 7, wherein the second insulating film includes a nitrided oroxidized material of at least one of tantalum, silicon, titanium,copper, tungsten, aluminum, hafnium, boron, cobalt, and carbon nanotube.9. The magnetic memory according to claim 6, wherein the second contactplug has a hollow structure in which a hollow space is provided along aheight direction.
 10. The magnetic memory according to claim 9, whereinthe hollow structure is a hollow cylinder.
 11. The magnetic memoryaccording to claim 9, wherein the first contact plug contacts the secondcontact plug at two points in a cross section of the first and secondcontact plugs taken along a plane defined by a normal direction which isperpendicular to a stacking direction of the first and second contactplugs.
 12. The magnetic memory according to claim 6, wherein the secondcontact plug includes an L-shaped portion.
 13. The magnetic memoryaccording to claim 6, wherein the magnetoresistive element is a MTJ(Magnetic Tunnel Junction) element.
 14. A method for manufacturing amagnetic memory comprising: forming a first insulating film on asubstrate; forming a first contact plug in the first insulating film;forming a second insulating film on the first insulating film; forming asecond contact plug connected to the first contact plug in the secondinsulating film, the second contact plug having a smaller diameter thana diameter of the first contact plug; forming stacked films to beprocessed into a magnetoresistive element on the second contact plug andthe second insulating film; and forming the magnetoresistive element byprocessing the stacked films.
 15. The method according to claim 14,wherein the first and second insulating films comprise a same material.16. A method for manufacturing a magnetic memory comprising: forming afirst insulating film on a substrate; forming a first contact hole inthe first insulating film; filling the first contact hole with a firstcontact plug; turning an upper part of the first contact hole into atrench unfilled with the first contact plug by removing an upper part ofthe first contact plug; forming a second insulating film on a part ofthe first contact plug and forming a second contact hole which reachesthe first contact plug and is surrounded by the second insulating film;filling the second contact hole with a second contact plug; formingstacked films to be processed into a magnetoresistive element on thesecond contact plug and the second insulating film; and forming themagnetoresistive element by processing the stacked films.
 17. The methodaccording to claim 16, wherein the first insulating film comprises amaterial differing from a material of the second insulating film.